This invention relates generally to a fluid retarder, and more particularly, to a method and apparatus for calibrating a fluid retarder located on a vehicle.
Vehicles such as off-highway trucks often use a fluid retarder to assist in slowing the vehicle, without operating the service brakes. A fluid retarder includes a rotor that is mechanically attached to a drive shaft and a retarder valve that enables fluid to flow across the rotor in a manner that slows the speed of the rotor, thereby slowing the speed of the drive train. Movement of the rotor through the fluid converts horse power into heat. That is, the fluid retarder may absorb torque created by the vehicle mass driving the drivetrain, thereby reducing the speed of the vehicle. Accurate control of the fluid retarder, in particular the retarder valve, is necessary in order to provide the desired resistance to assist in slowing the vehicle.
In previous systems the fluid retarder valve was manually calibrated at a service center which was a time consuming process. In addition, manual calibration generally does not provide the desired accuracy with regard to control of the fluid retarder. For example, in some previous systems, the retarder valve was controlled by a switch arrangement that controlled separate electrical solenoids which in turn moved the spool in the retarder valve to positions corresponding to the selected retarding levels. These arrangements did not provide accurate control of the fluid in the retarder cavity and therefore the retarding levels were not consistent. In newer arrangements the retarder valve is controlled by switches which send electrical signals to an electronic controller which in turn sends an electrical signal to a proportional electrical solenoid. The use of a proportional solenoid allows for more accurate control of the retarder, but requires accurate calibration.
In some systems air was used to actuate the retarder valve instead of hydraulic fluid. However, calibration of these systems was also manual, and lacked the desired calibration accuracy.
The present invention is directed to overcoming one or more of the problems identified above.
In one aspect of the present invention, a method for calibrating a fluid retarder in a transmission system is provided. The method includes the steps of delivering a valve command to the retarder valve, determining a speed of the engine, and calibrating the retarder valve in response to the valve command and the speed.
In another aspect of the present invention, an apparatus adapted to calibrate a fluid retarder in a transmission system is disclosed. The transmission system includes an engine connected to a transmission through a driveshaft. The fluid retarder includes a rotor mechanically connected to the driveshaft, and a retarder valve adapted to enable fluid flow across the rotor. The transmission system also includes, a speed sensing device, and a controller adapted to receive a speed signal, generate a valve command signal, determine an engine speed in response to the speed signal, and calibrate the retarder valve in response to the speed signal, and the valve command.